Filler wire position control

ABSTRACT

A system and method for controlling the position of a filler wire and/or a laser head, or other heating head, in a welding system. The distal end of the filler wire is gradually moved, e.g., upward, until electrical continuity with the weld pool is lost; the filler wire is then moved back into contact with the weld pool. The heating head may be stationary relative to the weld pool, or it may move, with the distal end of the filler wire, relative to the weld pool.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and the benefit of U.S.Provisional Application No. 62/625,909, filed Feb. 2, 2018, entitled“CONTROL FOR ADDITIVE WELDING”, the entire content of which isincorporated herein by reference.

FIELD

One or more aspects of embodiments according to the present inventionrelate to welding, and more particularly to a system and method forcontrolling the position of a filler wire and/or the position of aheating head in a welder.

BACKGROUND

Laser additive welding uses a laser beam to melt a consumable fillermaterial to additively increase the volume of the substrate. When theconsumable is in wire form, continuous operator monitoring andadjustment may be used to ensure correct laser beam focal point, fillerwire entry point and that the substrate is aligned in a thermallyoptimum fashion to ensure weld quality. This continuous monitoring mayrequire human operator feedback for the duration of the weld or the useof a sophisticated machine-vision-based control system, both of whichmay significantly increase the cost of performing the weld. Similarissues exist when other heat sources are used, i.e., the heating head isnot a laser head but, e.g., a plasma welding head.

Thus, there is a need for an improved system and method for controllingthe position of a filler wire and/or the position of a heating head in awelder.

SUMMARY

According to an embodiment of the present disclosure there is provided amethod for adjusting the position of a filler wire relative to a weldpool during welding, the method including: determining whether anelectrical continuity criterion, for electrical continuity between thefiller wire and the weld pool, is met; moving a distal end of the fillerwire in a first direction relative to the weld pool, while theelectrical continuity criterion is met, the first direction beingselected to cause the electrical continuity criterion to cease to bemet; and when the electrical continuity criterion ceases to be met,moving the distal end of the filler wire in a second direction relativeto the weld pool, the second direction being selected to cause theelectrical continuity criterion to be met.

In one embodiment, the method includes: moving a substrate, includingthe weld pool, in a third direction relative to a heating head;supplying heat from the heating head to the substrate and to the weldpool, wherein the first direction is: within 30 degrees of a linebetween the weld pool and the heating head; and at least 30 degrees fromthe third direction.

In one embodiment, the heating head is vertically above the weld pool,the first direction is vertically up, the second direction is verticallydown, and the third direction is horizontal.

In one embodiment, the moving of the distal end of the filler wire inthe first direction relative to the weld pool includes moving the distalend of the filler wire relative to a weld pool at a speed that is:greater than one hundredth of the speed of the moving of the substratein the third direction relative to the heating head, and less than onehalf of the speed of the moving of the substrate in the third directionrelative to the heating head.

In one embodiment, the moving of the distal end of the filler wire inthe second direction relative to the weld pool includes moving thedistal end of the filler wire through a fixed distance relative to theweld pool.

In one embodiment, the filler wire is a round wire having a diameter,and wherein the fixed distance is greater than 0.5 times the diameterand less than 1.5 times the diameter.

In one embodiment, the moving of the distal end of the filler wirethrough the fixed distance relative to the weld pool includes moving thedistal end of the filler wire through the fixed distance during a timeinterval shorter than 0.5 seconds.

In one embodiment, the electrical continuity criterion is met when theresistance between the filler wire and the weld pool is less than athreshold.

In one embodiment, the threshold is greater than 100 ohms.

In one embodiment, the determining of whether the electrical continuitycriterion is met includes: connecting a direct current source across thefiller wire and the weld pool, and determining the voltage drop acrossthe filler wire and the weld pool.

In one embodiment, the direct current source includes a voltage sourceconnected in series with a resistor, and wherein the determining of thevoltage drop across the filler wire and the weld pool includes measuringthe voltage drop across the resistor, and subtracting the measuredvoltage drop from a nominal output voltage of the voltage source.

In one embodiment, the weld pool is in a substrate; the method furtherincludes supplying heat from a heating head to the substrate and to theweld pool, and the moving of the distal end of the filler wire in thefirst direction relative to the weld pool includes: moving the heatinghead in the first direction relative to the weld pool; and maintainingthe position of the heating head relative to the distal end of thefiller wire constant.

In one embodiment, the heating head is a laser head.

In one embodiment, the method includes maintaining the position of thedistal end of the filler wire relative to the weld pool constant, beforethe moving of the distal end of the filler wire in the first directionrelative to the weld pool, and before the moving of the distal end ofthe filler wire in the second direction relative to the weld pool.

According to an embodiment of the present disclosure there is provided asystem for welding, the system including: a heating head for heating asubstrate; a conductive substrate attachment for forming a conductiveconnection to the substrate; a filler wire; a circuit for determiningwhether an electrical continuity criterion, for electrical continuitybetween the filler wire and the substrate, is met; and a filler wirerelative position control system, the filler wire relative positioncontrol system being configured, in operation, to move a distal end ofthe filler wire in a first direction relative to a weld pool on thesubstrate, while the electrical continuity criterion is met, the firstdirection being selected to cause the electrical continuity criterion tocease to be met; and when the electrical continuity criterion ceases tobe met, to move the distal end of the filler wire in a second directionrelative to the weld pool, the second direction being selected to causethe electrical continuity criterion to be met.

In one embodiment, the position control system is further configured tomove the substrate in a third direction relative to the heating head;and the moving of the distal end of the filler wire in the firstdirection relative to the weld pool includes moving the distal end ofthe filler wire relative to a weld pool at a speed that is: greater thanone hundredth of the speed of the moving of the substrate in the thirddirection relative to the heating head, and less than one tenth of thespeed of the moving of the substrate in the third direction relative tothe heating head.

In one embodiment, the moving of the distal end of the filler wire inthe second direction relative to the weld pool includes moving thedistal end of the filler wire through a fixed distance relative to theweld pool.

In one embodiment, the system includes a conductive sleeve surroundingthe filler wire and connected to the circuit for determining whether theelectrical continuity criterion is met.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will beappreciated and understood with reference to the specification, claims,and appended drawings wherein:

FIG. 1A is a schematic drawing of a weld in progress, according to anembodiment of the present invention;

FIG. 1B is a schematic drawing of a weld in progress, according to anembodiment of the present invention;

FIG. 1C is a schematic drawing of a weld in progress, according to anembodiment of the present invention;

FIG. 1D is a schematic drawing of a weld in progress, according to anembodiment of the present invention;

FIG. 2 is an illustration of a filler wire trajectory, according to anembodiment of the present invention; and

FIG. 3 is a block diagram of a welding system, according to anembodiment of the present invention.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of asystem and method for filler wire position control provided inaccordance with the present invention and is not intended to representthe only forms in which the present invention may be constructed orutilized. The description sets forth the features of the presentinvention in connection with the illustrated embodiments. It is to beunderstood, however, that the same or equivalent functions andstructures may be accomplished by different embodiments that are alsointended to be encompassed within the scope of the invention. As denotedelsewhere herein, like element numbers are intended to indicate likeelements or features.

Referring to FIGS. 1A-1D, in some embodiments, as a weld progressesacross a substrate 110, a laser head 120 focuses light into a smallfocal volume near the laser head 120 and forms a weld pool 130, andfiller metal is added by feeding a filler wire 140 into the weld pool130 as the weld progresses. The height of the weld head 150 (whichincludes the laser head 120 and a filler wire feed unit that feeds thefiller wire 140) may at a first point in time (illustrated in FIG. 1A)be sufficiently high above the substrate 110 that the filler wire 140 isnot in contact with the weld pool 130. This condition may be detected bytesting for electrical continuity between the filler wire 140 and thesubstrate 110. When a loss of electrical continuity between the fillerwire 140 and the substrate 110 is detected, the weld head 150 may belowered by an amount sufficient to reestablish electrical continuitybetween the filler wire 140 and the substrate 110, so that at a secondpoint in time (illustrated in FIG. 1B) the filler wire 140 is inphysical and electrical contact with the weld pool 130. The weld head150 may then be gradually raised, so that at a third point in time(illustrated in FIG. 1C) the filler wire 140 is higher, but remains inphysical and electrical contact with the weld pool 130, until, at fourthpoint in time (illustrated in FIG. 1D) the filler wire 140 is again notin contact with the weld pool 130, and electrical continuity between thefiller wire 140 and the substrate 110 has been lost. The process maythen be repeated, with the weld head 150 being lowered wheneverelectrical continuity is lost, and the weld head 150 being graduallyraised when electrical continuity is present between the filler wire 140and the substrate 110.

FIG. 2 shows the trajectory of the tip, or “distal end” of the fillerwire 140, in one embodiment, as a weld progresses from left to rightover the substrate. The substrate may have a nominal surface 210 (whichmay, for example, be flat, as shown), and the actual surface 220 maydiffer from the nominal surface, for example, as a result ofimperfections in the process used to fabricate the substrate. Forexample, if the substrate is formed by depositing material, on a pieceof metal initially fabricated to high precision, using a plurality ofwelding passes, each pass after the first being used to depositadditional material on top of the material deposited during thepreceding pass, variations in the thickness of the weld beads mayaccumulate, resulting in height variations in the top surface 220 of thesubstrate. As the weld progresses, the weld pool 130 may extend to someheight above the actual surface so that height 230 of the distal end ofthe filler wire 140 at which electrical continuity would be lost may beat some height above the actual surface 220 of the substrate, as shown.The radius of the filler wire 140 may also contribute to the height 230at which continuity is lost, if for example the height of the distal endof the filler wire 140 is defined to be the height of the center of thedistal end of the filler wire 140.

As shown in FIG. 2, if the filler wire 140 is gradually raised wheneverelectrical continuity is present between the filler wire 140 and thesubstrate 110, and lowered (e.g., lowered relatively quickly) wheneverelectrical continuity is lost between the filler wire 140 and thesubstrate 110, the distal end of the filler wire 140 may follow atrajectory 240 as shown, consisting of a plurality of gradually upwardsloping (or “rate climb”) first segments 250 (each of which ends whenthe distal end of the filler wire 140 reaches the height 230 at whichelectrical continuity is lost) and a plurality of more steeply downwardsloping second segments 260. During at least part of each first segment250, the direction of motion of the filler wire 140 relative to the weldpool 130 is such that the distance between the center of the distal endof the filler wire 140 and the centroid of the weld pool 130 isincreasing, and during at least part of each second segment 260, thedirection of motion of the filler wire 140 relative to the weld pool 130is such that the distance between the center of the distal end of thefiller wire 140 and the centroid of the weld pool 130 is decreasing,

During each of the upward sloping first segments 250 the distal end ofthe filler wire may be raised gradually (e.g., by raising the fillerwire (or the filler wire feed unit) alone, or by raising the weld head,including the laser head and the filler wire), e.g., at a rate of about¼ inch of height change per foot of (horizontal) travel of thesubstrate. During this time the electrical continuity between thesubstrate 110 and filler wire may be continuously monitored untilcontinuity is lost (when the distal end of the filler wire reaches theheight 230 at which electrical continuity is lost). When continuity islost the distal end of the filler wire may be lowered relativelyquickly, in a downward sloping second segment 260 (e.g., by lowering thefiller wire (or the filler wire feed unit) alone, or by lowering theweld head, including the laser head and the filler wire). During each ofthe downward sloping second segments 260 the distal end of the fillerwire may be lowered by a fixed amount (e.g., by 80% of the diameter ofthe filler wire, or, for example, by 0.008 inches for filler wire with adiameter of 0.010 inches), and it may be lowered relatively quickly(e.g., within 100 ms of the loss of continuity). The slope of the upwardsloping first segments 250 of FIG. 2 has been drawn to be considerablysteeper than ¼ inch of height change per foot of travel of thesubstrate, to make the slope more readily perceptible in the drawing.

The rate at which the filler wire is raised during the upward slopingfirst segments 250 may be adjusted to suit the task at hand. A higherrate may be better able to adjust to height variations in the substrate,whereas a lower rate may result in smoother deposition when the heightof the substrate is highly uniform. Similarly, the rate at which thefiller wire is lowered during the downward sloping second segments 260may be adjusted to suit the task at hand. In some embodiments the rateat which the filler wire is lowered during the downward sloping secondsegments 260 is adjusted to be as high as feasible within thelimitations of the actuators (described in further detail below) used toproduce the downward motion, to limit the time during which the fillerwire is not in contact with the weld pool, and thereby to avoidirregularities in the weld that may result if this time is excessive(and, for example, significant cooling of the distal end of the fillerwire occurs before contact with the weld pool is reestablished). In someembodiments, if the actuators controlling the position of the fillerwire 140 are capable of more rapid response (e.g., greater speed oracceleration) than the actuators controlling the laser head 120, it maybe advantageous to move the filler wire 140 as quickly as possible, sothat the time during which thermal contact between the weld pool and thefiller wire 140 is lost is as short as possible, even if doing so meansthat the motion of the laser head 120 lags behind that of the fillerwire 140 during the downward sloping second segments 260.

As discussed above, in some applications, height control according toembodiments of the present invention may be helpful for automaticallyallowing the filler wire 140 and/or the laser head 120 to follow heightvariations of the substrate (including any previously deposited layersof weld bead). In some such circumstances, variations in height may bethe only variations for which real-time (automatic or manual) control isneeded (e.g., the weld path may be substantially straight, and noreal-time control may be needed to adjust the position of the fillerwire 140 and/or the laser head 120 in the cross-weld direction), and insuch a situation embodiments of the present invention may make itpossible to avoid the use of a more costly (e.g., machine-vision-based)control system entirely. In addition to maintaining suitable filler wireheight, embodiments of the present invention in which the weld head 150is controlled as a unit (i.e., in which the laser head 120 and thefiller wire 140 are moved together) may be helpful for maintaining theheight of the focus of the laser beam relative to the weld pool.

When the nominal surface profile is not horizontal but sloped, the rateat which the filler wire is raised during the upward sloping firstsegments 250 may be adjusted accordingly. For example, the rate may bemade higher over portions of the substrate where the nominal surfaceslopes upward, so that, for example, the rate at which the filler wiremoves away from the weld pool is the same as it is when welding on ahorizontal portion of the substrate. Similarly, the rate at which thefiller wire is raised during the upward sloping first segments 250 maybe reduced over portions of the substrate where the nominal surfaceslopes downward. If the nominal surface of the substrate has asufficiently steep downward slope, the first segments may be horizontalor downward sloping, with a downward slope that is less (e.g., less by ¼inch per foot of weld) than the slope of the nominal surface of thesubstrate. In some embodiments, if the substrate is formed as describedabove, by depositing material on a piece of metal, using a plurality ofwelding passes, each pass after the first being used to depositadditional material on top of the material deposited during thepreceding pass, then a record may be kept of the trajectory of thedistal end of the filler wire during each pass, and this trajectory (ora modified version of the trajectory, e.g., a version that has beensmoothed and to which an offset, reflecting a typical height differencebetween the height of the distal end of the filler wire during a passand the height of the weld bead formed by the pass, has been added) maybe used as the nominal surface profile during the next pass.

Referring to FIG. 3, in some embodiments a welding system includes, asmentioned above, the laser head 120, and a filler wire feed unit 310 forsupplying the filler wire 140 to the weld pool 130. The system furthermay include a plurality of position actuators 315 (labeled “PA”) forcontrolling the position of the substrate 110, the laser head 120, andthe distal end of the filler wire 140. The welding system may alsoinclude a control circuit 325, including (i) a position actuator drivecircuit 330, for interfacing to the position actuators 315, (ii) a wirefeed drive circuit 335, for controlling the feed speed of the fillerwire 140, (iii) a continuity monitoring circuit 340 for determiningwhether electrical continuity is present between the filler wire 140 andthe weld pool 130, and (iv) a processing circuit 345 (described infurther detail below) for performing high-level control functions suchas commanding the position actuators 315 connected to the filler wirefeed unit 310 to move up or down depending on whether, as determined bythe continuity monitoring circuit 340, electrical continuity is presentbetween the filler wire 140 and the weld pool 130. The system may alsoinclude other elements (not shown) such as a laser power supply andcontroller, and a user interface device.

Two position actuators 315 are shown in FIG. 3 controlling the positionof the substrate 110, but more or fewer may be used. For example, threeposition actuators 315 may be used, to control position along threeorthogonal directions (e.g., “translational degrees of freedom”, thatmay be referred to as X, Y, and Z) or six position actuators 315 may beused to control three rotational degrees of freedom in addition to thethree translational degrees of freedom, or more than six positionactuators 315 may be used, providing a redundant capability to controlone or more degrees of freedom. Similarly the position of the laser head120 may be controlled by two position actuators 315, or by more or fewerposition actuators 315. As used herein, the “laser head” is one or moreoptical elements that determine the position of focal volume withinwhich the laser light is capable of producing significant heating.Moving optical elements so that the focal volume moves (relative to thesubstrate 110 and/or the filler wire 140) is referred to herein forbrevity as “moving the laser head”, although in some embodiments themoving of the focal volume may be accomplished by moving one or moremirrors and/or lenses within the laser. Two position actuators 315, ormore or fewer position actuators 315, may be mechanically connected tothe filler wire feed unit 310 and used to control the position of thedistal end of the filler wire 140. In some embodiments the position ofthe entire filler wire feed unit 310 is controlled by position actuators315 connected to it. In other embodiments the position actuators 315 areconnected instead to a smaller, movable element, such as a sleeve (e.g.,a conductive sleeve 320, discussed in further detail below) throughwhich the filler wire 140 passes, and which may be used to control theposition of the distal end of the filler wire 140 without moving theentire filler wire feed unit 310.

It will be understood that motion of the system as a whole generallywill have little or no effect on the welding operation, and that it isthe relative positions and velocities of elements of the system, such asthe substrate 110, the weld pool 130, the distal end of the filler wire140, and the laser head 120 that affect the weld. As such, “moving” afirst element relative to a second element may be accomplished either bychanging the position of the first element (e.g., with position or speedactuators connected to the first element) or by changing the position ofthe second element, or by changing the position of one of the firstelement and the second element by a first amount, and changing theposition of the other of the first element and the second element by asecond amount, different from the first amount. Accordingly, in someembodiments one or more elements of the substrate 110, the laser head120 and the filler wire 140 have no position actuators 315 and relativemotion is accomplished by moving other elements. For example, instead ofmoving the filler wire 140 and laser head along the filler wiretrajectory 240 (FIG. 2), the substrate 110 may be moved horizontally(e.g., at constant speed) to produce the horizontal component of therelative motion along the trajectory 240 and the filler wire 140 (or thefiller wire 140 and the laser head 120) may be moved vertically (e.g.,gradually up during the first segments 250 of the trajectory and down,more rapidly, during the second segments 260 of the trajectory) toproduce the vertical component of the relative motion along thetrajectory 240. In other embodiments the substrate 110 is stationary andthe filler wire 140 and the laser head 120 move across the substrate110, with a height profile according to the trajectory 240, or the wire140 and the laser head 120 are stationary and the substrate 110 moveshorizontally and vertically so that the relative position of thesubstrate 110 and the filler wire 140 follows the trajectory 240. Insome embodiments the feed speed of the filler wire feed unit 310 may becontrolled (through the wire feed drive circuit 335) as an additionalmethod for moving the distal end of the filler wire 140 relative to thesubstrate 110, in a direction that is parallel to the filler wire 140 atthe distal end of the filler wire 140.

In some embodiments the filler wire 140 or the laser head 120 may alsobe caused to move laterally (e.g., in a horizontal directionperpendicular to the direction of the weld), to achieve automatedalignment of these elements to the desired weld path. On a planarhorizontal substrate such lateral motion may not be effective to causerelative motion, and eventual loss of electrical continuity, between thefiller wire 140 and the weld pool, because the weld pool may simplyfollow the filler wire 140. If, however, the filler wire is movedrelative to the laser head 120, electrical continuity may eventually belost, and a method similar to that described above, resulting in afiller wire trajectory that is horizontal but otherwise analogous tothat of FIG. 2 may result. In another embodiment, if a weld is to beformed on top of a sufficiently steep and narrow ridge, lateral motionof the weld pool may be constrained by the sloping portions of theridge, and for this reason the weld pool may not follow the filler wire140 even if the laser head 120 is moved laterally with the filler wire140. Such lateral control (performed by introducing lateral positionchanges until continuity is lost) may be used alternately with thevertical control described above, with, for example, each pair ofvertical segments (a first segment 250 and a second segment 260) beingfollowed by an analogous pair of lateral segments.

Contact between the continuity monitoring circuit 340 and filler wire140 may be established in any of several ways, including (as shown)through the conductive sleeve 320 through which the filler wire may pass(and be in contact with) or through conductive (metal) rollers betweenwhich the filler wire may pass. Contact between the continuitymonitoring circuit 340 and the substrate 110 may be established by aconductive substrate attachment 350, which may be a clamp, for clampinga wire to the substrate 110, or a collection of elements providing aconductive path between the continuity monitoring circuit 340 and thesubstrate 110, such as a metal motion-control table to which thesubstrate 110 is secured, metal clamps securing the substrate 110 to themotion-control table, and one or more wires connecting the continuitymonitoring circuit 340 to the motion-control table and bridging anynonconductive elements in the mechanical load path supporting thesubstrate 110.

The continuity monitoring circuit 340 may be any device suitable forapplying a voltage and/or a current to the substrate 110 and filler wire140 and for monitoring the resulting current flowing through the fillerwire 140 or the voltage across the substrate 110 and filler wire 140. Insome embodiments, a reference voltage of 24 V is applied, through aseries resistor, across the substrate 110 and filler wire 140, and thevoltage across the resistor and/or across the substrate 110 and fillerwire 140 is measured, e.g., with an analog to digital converter. Whenthe voltage drop is primarily across the resistor (i.e., the voltagedrop across the resistor is substantially equal to 24 V), the system mayinfer that there is continuity between the substrate 110 and filler wire140, and when the voltage drop is primarily across the substrate 110 andfiller wire 140 (i.e., the voltage drop across the resistor issubstantially equal to 0 V) the system may infer that there is nocontinuity between the substrate 110 and filler wire 140.

In some embodiments, the continuity monitoring circuit 340 includes apremonition circuit that is used to detect an imminent loss ofelectrical continuity, either by detecting that the resistance betweenthe filler wire 140 and the substrate 110 has exceeded a threshold, orthat some quantity related to the resistance between the filler wire 140and the substrate 110 (e.g., the rate of change of resistance betweenthe filler wire 140 and the substrate 110) has exceeded a threshold. Theimminent loss of continuity may then operate as a trigger for a changein the relative motion of the filler wire 140 and the weld pool 130. Assuch, the criterion for determining when to change the direction ofmotion of the filler wire relative to the weld pool need not be acomplete loss of continuity (i.e., a transition from a near-perfectshort circuit to a near-perfect open circuit) and it may instead be adifferent criterion, such as the resistance between the filler wire 140and the substrate 110 exceeding a threshold, or the rate of change ofthe resistance between the filler wire 140 and the substrate 110exceeding a threshold. Such a criterion, on the resistance between thefiller wire 140 and the substrate 110, or on a quantity related to theresistance between the filler wire 140 and the substrate 110 (e.g., therate of change of resistance between the filler wire 140 and thesubstrate 110) may be referred to as an “electrical continuitycriterion, for electrical continuity between the filler wire and thesubstrate”, or (the weld pool generally being in good electrical contactwith the weld pool) as an “electrical continuity criterion, forelectrical continuity between the filler wire and the weld pool”.

In some embodiments a stuck wire detection circuit may be used as thecontinuity monitoring circuit 340. A stuck wire detection circuit may beincorporated in the laser welder to detect situations when the fillerwire is stuck to the weld at the end of a weld (so that, in such asituation, substrate motion, which may damage the equipment when thewire is stuck, may be avoided). In this case, an existing welder may bemodified to implement an embodiment of the present invention byprogramming it with a suitable algorithm, and without augmenting orotherwise modifying the hardware of the welder.

In some embodiments, the automatic control algorithm may be disabled(i.e., the filler wire height may be held constant, or manuallycontrolled) at the beginning of the weld (until a stable weld pool isestablished) and at the end of the weld (once the reduction of laserpower, at the end of the weld, begins).

Some embodiments may be used in an analogous manner with heat sourcesother than lasers, e.g., with an arc heat source (as in a tungsten inertgas (TIG) (or GTAW) welder), or with a plasma heat source, and the headof any such heat source may more generally be referred to as a “heatinghead” instead of the “laser head” mentioned in some examples describedherein. Embodiments of the present invention may be used to performstraight, horizontal welds, or other welds, e.g., sloping welds in whichthe weld head 150 maintains a vertical speed that is a significantfraction of the horizontal feed rate of the substrate, or welds thatinclude changes in direction. In such cases the motion of the weld head150 may be controlled by a combination of a preprogrammed trajectorythat follows the expected weld path, and corrections, provided by anembodiment of the present invention, to account for deviations from theexpected weld path.

The term “processing circuit” is used herein to mean any combination ofhardware, firmware, and software, employed to process data or digitalsignals. Processing circuit hardware may include, for example,application specific integrated circuits (ASICs), general purpose orspecial purpose central processing units (CPUs), digital signalprocessors (DSPs), graphics processing units (GPUs), and programmablelogic devices such as field programmable gate arrays (FPGAs). In aprocessing circuit, as used herein, each function is performed either byhardware configured, i.e., hard-wired, to perform that function, or bymore general purpose hardware, such as a CPU, configured to executeinstructions stored in a non-transitory storage medium. A processingcircuit may be fabricated on a single printed circuit board (PCB) ordistributed over several interconnected PCBs. A processing circuit maycontain other processing circuits; for example a processing circuit mayinclude two processing circuits, an FPGA and a CPU, interconnected on aPCB.

It will be understood that, although the terms “first”, “second”,“third”, etc., may be used herein to describe various elements,components, regions, layers and/or sections, these elements, components,regions, layers and/or sections should not be limited by these terms.These terms are only used to distinguish one element, component, region,layer or section from another element, component, region, layer orsection. Thus, a first element, component, region, layer or sectiondiscussed herein could be termed a second element, component, region,layer or section, without departing from the spirit and scope of theinventive concept.

Spatially relative terms, such as “beneath”, “below”, “lower”, “under”,“above”, “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. It will beunderstood that such spatially relative terms are intended to encompassdifferent orientations of the device in use or in operation, in additionto the orientation depicted in the figures. For example, if the devicein the figures is turned over, elements described as “below” or“beneath” or “under” other elements or features would then be oriented“above” the other elements or features. Thus, the example terms “below”and “under” can encompass both an orientation of above and below. Thedevice may be otherwise oriented (e.g., rotated 90 degrees or at otherorientations) and the spatially relative descriptors used herein shouldbe interpreted accordingly. In addition, it will also be understood thatwhen a layer is referred to as being “between” two layers, it can be theonly layer between the two layers, or one or more intervening layers mayalso be present.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the inventiveconcept. As used herein, the terms “substantially,” “about,” and similarterms are used as terms of approximation and not as terms of degree, andare intended to account for the inherent deviations in measured orcalculated values that would be recognized by those of ordinary skill inthe art. As used herein, the term “major component” refers to acomponent that is present in a composition, polymer, or product in anamount greater than an amount of any other single component in thecomposition or product. In contrast, the term “primary component” refersto a component that makes up at least 50% by weight or more of thecomposition, polymer, or product. As used herein, the term “majorportion”, when applied to a plurality of items, means at least half ofthe items.

As used herein, the singular forms “a” and “an” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising”, when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. As used herein, the term “and/or”includes any and all combinations of one or more of the associatedlisted items. Expressions such as “at least one of,” when preceding alist of elements, modify the entire list of elements and do not modifythe individual elements of the list. Further, the use of “may” whendescribing embodiments of the inventive concept refers to “one or moreembodiments of the present invention”. Also, the term “exemplary” isintended to refer to an example or illustration.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to”, “coupled to”, or “adjacent to” anotherelement or layer, it may be directly on, connected to, coupled to, oradjacent to the other element or layer, or one or more interveningelements or layers may be present. In contrast, when an element or layeris referred to as being “directly on”, “directly connected to”,“directly coupled to”, or “immediately adjacent to” another element orlayer, there are no intervening elements or layers present.

Any numerical range recited herein is intended to include all sub-rangesof the same numerical precision subsumed within the recited range. Forexample, a range of “1.0 to 10.0” is intended to include all subrangesbetween (and including) the recited minimum value of 1.0 and the recitedmaximum value of 10.0, that is, having a minimum value equal to orgreater than 1.0 and a maximum value equal to or less than 10.0, suchas, for example, 2.4 to 7.6. Any maximum numerical limitation recitedherein is intended to include all lower numerical limitations subsumedtherein and any minimum numerical limitation recited in thisspecification is intended to include all higher numerical limitationssubsumed therein.

Although exemplary embodiments of a system and method for filler wireposition control have been specifically described and illustratedherein, many modifications and variations will be apparent to thoseskilled in the art. Accordingly, it is to be understood that a systemand method for filler wire position control constructed according toprinciples of this invention may be embodied other than as specificallydescribed herein. The invention is also defined in the following claims,and equivalents thereof.

What is claimed is:
 1. A method for adjusting the position of a fillerwire relative to a weld pool during welding, the method comprising:determining whether an electrical continuity criterion, for electricalcontinuity between the filler wire and the weld pool, is met; moving adistal end of the filler wire in a first direction relative to the weldpool, while the electrical continuity criterion is met, the firstdirection being selected to cause the electrical continuity criterion tocease to be met; and when the electrical continuity criterion ceases tobe met, moving the distal end of the filler wire in a second directionrelative to the weld pool, the second direction being selected to causethe electrical continuity criterion to be met.
 2. The method of claim 1,further comprising: moving a substrate, comprising the weld pool, in athird direction relative to a heating head; supplying heat from theheating head to the substrate and to the weld pool, wherein the firstdirection is: within 30 degrees of a line between the weld pool and theheating head; and at least 30 degrees from the third direction.
 3. Themethod of claim 2, wherein: the heating head is vertically above theweld pool, the first direction is vertically up, the second direction isvertically down, and the third direction is horizontal.
 4. The method ofclaim 2, wherein the moving of the distal end of the filler wire in thefirst direction relative to the weld pool comprises moving the distalend of the filler wire relative to a weld pool at a speed that is:greater than one hundredth of the speed of the moving of the substratein the third direction relative to the heating head, and less than onehalf of the speed of the moving of the substrate in the third directionrelative to the heating head.
 5. The method of claim 1, wherein themoving of the distal end of the filler wire in the second directionrelative to the weld pool comprises moving the distal end of the fillerwire through a fixed distance relative to the weld pool.
 6. The methodof claim 5, wherein the filler wire is a round wire having a diameter,and wherein the fixed distance is greater than 0.5 times the diameterand less than 1.5 times the diameter.
 7. The method of claim 5, whereinthe moving of the distal end of the filler wire through the fixeddistance relative to the weld pool comprises moving the distal end ofthe filler wire through the fixed distance during a time intervalshorter than 0.5 seconds.
 8. The method of claim 1, wherein theelectrical continuity criterion is met when the resistance between thefiller wire and the weld pool is less than a threshold.
 9. The method ofclaim 8, wherein the threshold is greater than 100 ohms.
 10. The methodof claim 1, wherein the determining of whether the electrical continuitycriterion is met comprises: connecting a direct current source acrossthe filler wire and the weld pool, and determining the voltage dropacross the filler wire and the weld pool.
 11. The method of claim 10,wherein the direct current source comprises a voltage source connectedin series with a resistor, and wherein the determining of the voltagedrop across the filler wire and the weld pool comprises measuring thevoltage drop across the resistor, and subtracting the measured voltagedrop from a nominal output voltage of the voltage source.
 12. The methodof claim 1, wherein: the weld pool is in a substrate; the method furthercomprises supplying heat from a heating head to the substrate and to theweld pool, and the moving of the distal end of the filler wire in thefirst direction relative to the weld pool comprises: moving the heatinghead in the first direction relative to the weld pool; and maintainingthe position of the heating head relative to the distal end of thefiller wire constant.
 13. The method of claim 12, wherein the heatinghead is a laser head.
 14. The method of claim 1, further comprisingmaintaining the position of the distal end of the filler wire relativeto the weld pool constant, before the moving of the distal end of thefiller wire in the first direction relative to the weld pool, and beforethe moving of the distal end of the filler wire in the second directionrelative to the weld pool.
 15. A system for welding, the systemcomprising: a heating head for heating a substrate; a conductivesubstrate attachment for forming a conductive connection to thesubstrate; a filler wire; a circuit for determining whether anelectrical continuity criterion, for electrical continuity between thefiller wire and the substrate, is met; and a filler wire relativeposition control system, the filler wire relative position controlsystem being configured, in operation, to move a distal end of thefiller wire in a first direction relative to a weld pool on thesubstrate, while the electrical continuity criterion is met, the firstdirection being selected to cause the electrical continuity criterion tocease to be met; and when the electrical continuity criterion ceases tobe met, to move the distal end of the filler wire in a second directionrelative to the weld pool, the second direction being selected to causethe electrical continuity criterion to be met.
 16. The system of claim15, wherein: the position control system is further configured to movethe substrate in a third direction relative to the heating head; and themoving of the distal end of the filler wire in the first directionrelative to the weld pool comprises moving the distal end of the fillerwire relative to a weld pool at a speed that is: greater than onehundredth of the speed of the moving of the substrate in the thirddirection relative to the heating head, and less than one tenth of thespeed of the moving of the substrate in the third direction relative tothe heating head.
 17. The system of claim 15, wherein the moving of thedistal end of the filler wire in the second direction relative to theweld pool comprises moving the distal end of the filler wire through afixed distance relative to the weld pool.
 18. The system of claim 15,further comprising a conductive sleeve surrounding the filler wire andconnected to the circuit for determining whether the electricalcontinuity criterion is met.